To learn more about the predictive power of scientific theories and fossil evidence by studying the evolution of feathers.
This lesson is based on the highly engaging book Feathers: The Evolution of a Natural Miracle, by biologist Thor Hanson. The book is one of the winners of the 2012 SB&F Prize for Excellence in Science Books. SB&F, Science Books & Films, is a project of the American Association for the Advancement of Science. Due to the normal demands on class time, you might want to consider using this lesson with an advanced group of students, or as extra credit for highly motivated and focused students. Because this lesson pairs nicely with the ScienceNetlinks' Introduction to Natural Selection lesson, please use that lesson as a prerequisite for this one.
In the 15 chapters of Feathers, Hanson details a sweeping natural history of feathers as he investigates their function in birds of insulating, cooling, waterproofing, enabling prolonged efficient flight, attracting mates, and protecting birds through camouflage. The book ranges from the discovery of feathered dinosaurs that provided the first evidence linking them as the relatives of birds, to the valuable plumes onboard the Titanic, to the problems a feather costume poses to Las Vegas show dancers. The colorful stories are woven together with careful descriptions of scientific experiments, field observations shaped into scientific hypotheses, and an extensive research bibliography.
The lesson is intended to help students meet learning goals by understanding:
- The role that variation within a species of organism plays, which is to maximize survival of some members under changing environmental conditions. Feathers' ability to provide insulation, cooling, flight, courtship communication, and protective coloration are to be explored in this lesson as having the potential for adaptive advantage to increase survival.
- How theory and experimental or field evidence support the classification system scientists use to determine the degree of relatedness between organisms, in this case, birds and dinosaurs.
You should be alert for a common misconception that many learners have about evolution:
Research into common misconceptions shows that natural selection, adaptation, and evolution are challenging concepts for high-school and college students. Confusion frequently stems from students’ inability to integrate the two distinct processes in evolution: 1) the emergence of novel traits in a population and 2) their effect on long-term survival of the species. Many students believe that new traits are planned and purposeful—that is, "the animal flies because it needs to." They have little understanding that evolution proceeds by random changes in gene expression that affect future generations—and that changes are not always "positive" or an advantage. Chance alone produces new heritable characteristics by forming new combinations of existing genes or by mutations of genes that delete them, add extra copies, or otherwise alter their expression of the directions they make for the coding of proteins. Some students erroneously believe that a mutation modifies an individual's own form during its life rather than only its germ cells and offspring (see almost any science-fiction movie). (Benchmarks for Science Literacy, pp. 343-344.)
Students also have difficulties understanding that changing a population results from the survival of a few optimally adapted individuals who therefore have a survival advantage that allows them to reproduce more successfully than others. Change does not occur gradually among all individuals in the population. It is helpful to note that in everyday usage, individuals adapt deliberately—they decide to change. But in the theory of natural selection, populations change or "adapt" over generations, inadvertently. Students of all ages often erroneously believe that adaptations result from some overall purpose or design. Or they describe adaptation as a conscious process to fulfill some need or want. Research on understanding evolution suggests that students’ comprehension of the concept is related to their grasp on the nature of science and their general reasoning abilities. Findings indicate that poor reasoners tend to retain nonscientific beliefs such as “evolutionary change occurs as a result of need” because they fail to examine alternative hypotheses and their predicted consequences, and they fail to comprehend conflicting evidence. Thus, they are left with no alternative but to believe their initial intuitions or the misstatements they hear. (Benchmarks for Science Literacy, pp. 343-344.)
Though engaging, the book is 336 pages. In 15.5 minutes, though, you can get a good grounding of its main points by listening to the interview Feathers – Thor Hanson Interview on CBC Radio. Then read the National Geographic article, Feather Evolution and you'll have the gist that allows you to read the book quickly and easily.
For the bulk of the lesson, students will read the book, and then participate in a group "Grab Bag Book Report" as an Assessment. You have the option to assign them to write a short essay (five paragraphs) of key scientific and evolutionary ideas in the book.
If that's not possible to have one copy of the book per student, obtain several copies for groups to share in class and homework reading. One copy for you to read portions of aloud and pass to other student readers also works.
On an overhead projector, display two images from the book, or photocopy enough for each pair of learners or individual students and hand out. One image shows contour feather morphology, found on p. 275. The other shows the feather tracts on the bird body from which feathers emerge, on p. 110. Ask students to study them.
Next, engage students in the topic and check for their prerequisite knowledge with a Feather Discovery exercise. Either:
- Obtain from the local science museum or bird-watching group various types of feathers to show to students and ask them to reflect on them and jot four observations/sensations. OR,
- Pass out one feather from a bag of purchased craft feathers to each student, and ask him or her to ponder it and jot four observations/sensations.
As they explore the displayed images, draw in their notebooks, think about feathers, and experience them with the senses, have them listen as a group to a CBC interview with the author, Feathers – Thor Hanson Interview on CBC Radio. Students also can use the Feathers student esheet to listen to the interview.
At the end of Feather Discovery, ask each student to share one observation during classroom round-robin. Follow-up by asking probing questions to evaluate their level of understanding, and to correct misconceptions. Answers to these questions are on the Feathers teacher sheet. Students can record their answers to these questions on the Feathers student sheet.
- The author is a scientist, but chooses an unscientific word "miraculous" for the title. This word is unscientific because it refers to an awe-inspiring inexplicability of phenomena. Yet Hanson spends 336 pages with lots of data and field reports to frame a data-based argument for the evolution of feathers. Huh? What might another good title be for a book or article on feather evolution?
- Name four functions feathers perform to help birds thrive and survive.
- Briefly summarize the Ground-up Theory of Flight.
- What is the traditional view of how feathers evolved?
- How is the new theory different?
- What do Las Vegas dancers have in common with birds?
- Name three roles feathers have played in human cultures of the world.
- Define Archaeopteryx. Why is it important to evolutionary debate?
- Define Sinosauropteryx. Why is it important to evolutionary debate?
- Define Rick Prum and Xu Xing. Why are they important to evolutionary debate?
Students should read the book, Feathers: The Evolution of a Natural Miracle either independently or in groups during class or as homework. Class structure and book availability will determine this.
As they read, students will complete the Feathers student sheet to help capture the main content ideas and use them for class discussion and a writing assignment. Encourage them to add and synthesize details to the student sheet from other sources of information besides the book, such as the CBC podcast they listened to during Feather Discovery, or these articles:
The Feathers teacher sheet will help guide discussion toward learning goals and reveal student misconceptions.
The students will demonstrate understanding through a fun and interactive "Grab Bag Book Review: An Interactive Report in 15 Objects." In this lively and engaging exercise described more fully on the Teacher Assessment Sheet, objects are plucked blindly from a grocery bag, one at a time, to act as prompts for re-telling big ideas in the book.
The Teacher Assessment Sheet helps guide responses to learning goals the book addresses of: 1) how the fossil record provides scientific evidence for modern understanding of evolution and natural history and 2) species diversity, and how it arises through evolution and natural selection.
After this exercise, assign a homework assessment of writing a short essay addressing one of two topics below:
- Author Hanson explores two main evolutionary theories on the relationship of birds to dinosaurs. Write a thesis statement that clearly sets out the relationship, and then develop three paragraphs that provide background, context, and evidence for it. Analyze the arguments by concluding with your own thoughts on whether you are persuaded by the evidence. Are you persuaded by the scientific evidence that birds are the descendants of dinosaurs? Why or why not?
- Author Thor Hanson is trained as a field biologist who greatly enjoys gathering scientific evidence and observations. Frequently in the book, he recounts his own first-hand experiences and experiments testing concepts. Write a thesis statement on the role that evidence, observation, and data play in scientific understanding. Give three examples of the experiments Hanson—or others in the book—conduct, and identify the ideas they are testing. Conclude with an analytical statement reflecting your opinion on how strong the evidence was that the experiments produced. If you were to replicate the experiments, would you do them exactly as described in the book—or modify them? If you were to modify them—how would you do it, and why? Express this last thought in the context of a hypothesis you create.
To further apply concepts in this lesson regarding the adaptive advantages feather properties can give a bird, work as a class or in small groups studying the following Web pages and discuss how you see feathers exhibit various functions—one site catalogues 23 functions! Find them! These include the role of color in mating and territorial dominance, waterproofing and regulating body temperature, and camouflaging for protection from predators.
To expand learning on ideas of evolution and natural selection, see these Science NetLinks lessons: